Carrier mounted drilling unit

ABSTRACT

Improvements in apparatus for drilling wells. The apparatus is particularly suitable for drilling exploration holes or shallow production holes up to about 2,500 or 3,000 feet in depth. The drilling unit is readily transportable from one site to another and is capable of carrying, on racks provided for the purpose, all the drill pipe required for the drilling of relatively shallow production holes or exploration holes. The drilling unit, including the drill pipe racks, is preferably arranged such that a major portion of the weight of the complete drilling unit including a full complement of drill pipe supported on the drill racks is available to produce downward thrust of the drill bit when drawdown forces are being applied to the drill string. The power source, the drive train and the propulsion wheels are located adjacent one end of the chassis thereby leaving the central region of the chassis free of drive train components and the like. It is in this central region that the drill mast and its associated equipment is located. An operators&#39;&#39; station is mounted on the chassis and means are provided to support the station for movement from a first position for transportation of the drilling unit wherein the operators&#39;&#39; station overlies a portion of the racking area to a second operating position dispolaced outwardly of the racking area whereby a ready access may be had to the latter for addition or withdrawal of drill stem as the case may be. The apparatus also includes means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm adapted to grasp and wing individual pipe sections between a generally upwardly directed position at or in the mast and a lower generally horizontal position. The apparatus includes storage means for the sections of drill pipe having a bed for supporting a plurality of layers of generally horizontally disposed pipe sections, the layers being in generally vertically stacked relation. Means are provided for raising or lowering the bed of the pipe storage means thereby to raise or lower the layers of pipe sections supported thereon to enable one of of said layers to be positioned adjacent the lower generally horizontal position taken by the pipe handling arm. Means are provided for individually transferring the sections of pipe from the storage means at the level of said pipe layer to the pipe handling arm for engagement thereby and vice versa.

United States Patent [191 Wilderman [54] CARRIER MOUNTED DRILLING UNIT [75] Inventor: Giles H. Wilderman, Calgary, Al-

berta, Canada [73] Assignee: Kenting Drilling Ltd., Calgary, Al-

berta, Canada [22] Filed: Apr. 20, 1971 [21] Appl. No.: 135,603

[30] Foreign Application Priority Data Primary Examiner-David H. Brown Attorney-Fleit, Gipple & Jacobson [57] ABSTRACT Improvements in apparatus for drilling wells. The apparatus is particularly suitable for drilling exploration holes or shallow production holes up to about 2,500 or 3,000 feet in depth. The drilling unit is readily transportable from one site to another and is capable of carrying, on racks provided for the purpose, all the drill pipe required for the drilling of relatively shallow [45! May 22,1973

production holes or exploration holes. The drilling unit, including the drill pipe racks, is preferably arranged such that a major portion of the weight of the complete drilling unit including a full complement of drill pipe supported on the drill racks is available to produce downward thrust of the drill bit when draw down forces are being applied to the drill string. The power source, the drive train and the propulsion wheels are located adjacent one end of the chassis thereby leaving the central region of the chassis free of drive train components and the like. lt is in this central region that the drill mast and its associated equipment is located. An operators station is mounted on the chassis and means are provided to support the station for movement from a first position for transportation of the drilling unit wherein the operators station overlies a portion of the racking area to a second operating position dispolaced outwardly of the racking area whereby a ready access may be had to the latter for addition or withdrawal of drill stem as the case may be. The apparatus also includes means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm adapted to grasp and wing individual pipe sections between a generally upwardly directed position at or in the mast and. a lower generally horizontal position. The apparatus includes storage means for the sections of drill pipe having a bed for supporting a plurality of layers of generally horizontally disposed pipe sections, the layers being in generally vertically stacked relation. Means are provided for raising or lowering the bed of the pipe storage means thereby to raise or lower the layers of pipe sections supported thereon to enable one of of said layers to be positioned adjacent the lower generally horizontal position taken by the pipe handling arm. Means are provided for individually transferring the sections of pipe from the storage means at the level of said pipe layer to the pipe handling arm for engagement thereby and vice versa.

26 Claims, 13 Drawing Figures PATENTED M21975 3,734,210

SHEET 1 BF 9 INVENTOR Giles Widerma BY j mfiau ATTORNEYS PATENTEBHAYZZ I975 SHEET 5 [IF 9 FIG.

P T T M 221975 g SHEET' 7 OF 9 PATENTEU 3,734,210

SHEET 9 [IF 9 CARRIER MOUNTED DRILLING UNIT BACKGROUND OF THE INVENTION This invention relates generally to improvements in apparatus for drilling wells particularly mobile well drilling apparatus. The apparatus is particularly suitable for drilling exploration holes or shallow production holes up to about 2,500 or 3,000 feet in depth, and for blast hole drilling.

One problem faced by manufacturers of mobile relatively light weight drilling equipment of the type under consideration is that of providing sufficient pressure on the drill bit when drilling shallow holes as to provide a reasonably fast rate of travel of the bit through the earths crust. In large drilling rigs for drilling in the 3,000l0,000 feet hole depth range this does not constitute a major problem as the necessary pressure on the drill bit may be supplied by the weight of the relatively long drill string itself. However, in drilling machines specially adapted for shallow hole drilling (-3,000 feet approximately) or in blast hole drilling, it has been found necessary to provide pull-down means for applying at least a portion of the weight of the entire drilling rig to the drill string and thus to the drill bit. Therefore, it is readily apparent that the greater the proportion of the weight of the entire drilling rig made available for applying downward thrust to the drill string, the greater the overall efficiency of the drilling apparatus. Since virtually all prior art mobile drilling equipment has utilized a design wherein the drilling axis is positioned at the rear, or occasionally at the front, of the machine they were capable of applying only a relatively small proportion of their weight to the drill bit. A major advance in the art came with the introduction of mobile drilling rigs having their components arranged such that the drilling axis thereof passes through or near to the center of gravity whereby to enable utilization of virtually all of the weight of the drilling unit to provide downward thrust on the drill string. Reference may be had here to the structure disclosed in Canadian Pat. No. 781,323 issued Mar. 26, 1968 and assigned to the assignee of the present invention. This patent discloses a lightweight drilling rig specially adapted for transportation from one drilling site to another by helicopter with the various components of the rig being arranged such that its drilling axis passes substantially through its center of gravity. In this way the drilling unit was made sufficiently light as to be transportable by helicopter and at the same time was capable of providing sufficient downward thrust on the drill bit as to provide for a reasonably fastdrilling rate.

SUMMARY OF THE INVENTION The present invention provides in a first aspect, a mobile drilling unit including an elongated mobile chassis and a drilling mast attached to the chassis and arranged for movement between a transport position and an operative drilling position. Means are included for rotatably supporting a drill string within the mast together with means for applying drawdown forces to the drill string support means. A drill pipe racking means and drill operating machinery are also mounted on the chassis. The racking means is capable of carrying a sufficient weight of drill pipe and the drilling machinery, drill mast and racking mans are arranged relative to one another such as to permit a major portion of the combined weight of the drilling unit and the weight of the drill pipe on said racking means to be made available to produce downward thrust on the drill string when drawdown forces are being applied to the means for rotatably supporting the same i.e. the center of gravity of the entire system is at or near to the drilling axis.

It will be appreciated that as the depth of the hole increases during drilling, the drill pipe on the racking device will be gradually used up as additional sections are added to the drill string; as a result "the center of gravity of the entire system will gradually be displaced away from the drilling axis. However, this does not create a problem, because as the hole becomes deeper the weight of the lengthening drill string becomes progressively greater with the result being that adequate downward thrust can be applied to the drill bit at all times. The need for the drilling axis to pass through the center of gravity of the drilling unit-racked drill pipe combination is greatest at the start-up of drilling operations when the length of the drill string is quite short. As the length of the drill string increases, the center of gravity of the racked drill pipe-drilling unit combination can shift away from the center of gravity of the system without creating any difficulty. Hence this aspect of the invention provides a self contained drilling unit, capable of carrying its own drill pipe and wherein the weight of the pipe is used to advantage particularly during the early stages of a well drilling operation. A further advantage of the above described arrangement wherein the racked drill pipe is supported on the drilling unit is that the drilling apparatus may be shifted from one drilling site to another while carrying its own drill pipe; there is usually no need for additional vehicles to carry the drill pipe. This reduces moving and set up costs and makes for a more economical operation. Since the weight of the drill pipe supported on the racks of the drilling unit is used to supply downward thrust to the drill bit, the overall weight of the remainder of the drilling unit is dictated solely by structural strength requirements i.e. there is absolutely no need to make the unit heavier than design requirements dictate solely for the purpose of providing additional weight to the unit which can be used to produce additional downward thrust on the drill.

As mentioned previously, prior art machines have been arranged such that the drilling axis is disposed at one end or other of the drilling unit for several reasons. In self-propelled mobile drilling units i.e. units including a power source connected by a drive train to one or more sets of propulsion wheels, the drive shaft and other various components of the drive train are located in the center section of the machine and thus would be in the way of any drilling mast and its associated equipment in this area. As a result there is a tendency to place the drill mast etc. at one end, preferably the rear end, of the unit.

The present invention .provides, in a further aspect, for a major change in the positioning and arrangement of the various components of the drilling rig. The invention provides for the power source, the drive train and the propulsion wheels to be located adjacent one end of the chassis thereby leaving the central region of the chassis free of drive train components and the like. It is in this central region that the drill mast and its associated equipment is located.

Accordingly therefore, in a further aspect of the invention, there is provided a self-propelled mobile drilling unit including an elongated chassis, sets of wheels mounted forwardly and rearwardly of said chassis, a drive engine mounted rearwardly on said chassis. Racking means are mounted on the chassis forwardly of said region in spaced relation therewith for storing lengths of drill pipe such that they extend longitudinally of the chassis. The drilling mast is connected to the chassis generally between the rearwardly disposed region and the racking means and is movable from an upright operating position to a downfolded position for transport, the drill mast including means for rotatably supporting a length of drill string therein. Means are included for rotating the drill string and supplying drawdown or lifting forces thereto. A drive train is positioned in the rearwardly disposed region and is adapted to provide an operable connection of the drive engine to either said rearwardly disposed set of wheels to effect propulsion of the drilling unit or to the means for rotating the drill string.

In accordance with a further aspect of the invention there is provided a mobile drilling unit including an elongated wheeled mobile chassis, a mast mounted on the chassis and means for rotatably supporting a drill string therein. The drill pipe racking area extends longitudinally of the chassis for storing lengths of drill pipe thereon and means are provided for pivoting lengths of drill pipe between the racking area and the mast for addition or withdrawal of the lengths of pipe from the drill string. An operators station is mounted on the chassis and means are provided to support the station for movement from a first position for transportation of the drilling unit wherein the operators station overlies a portion of the racking area to a second position displaced outwardly of the racking area whereby a ready access may be had to the latter for addition or withdrawal of drill stem as the case may be. In the preferred arrangement the supporting means is arranged such that the operators station moves in a path parallel to the longitudinal axis of the chassis. The operating position of the operators station during drilling is located outwardly, of the end of the elongated chassis.

By providing for a movable operators station the required overall length of the mobile drilling unit is reduced. This is important because if the drilling unit as a whole is overly long it is unwieldy and difficult to handle particularly when travelling along public highways or the like. With the above described arrangement the mobile drilling unit need only be made long enough so as to accommodate the mast and its associated drill operating machinery and the drill pipe racking means. There is no need for the operators station to take up additional space lengthwise of the drilling unit as it can overlie a portion of the drill pipe racking area during transportation and thereafter be displaced outwardly of the racking area during a drilling operation.

In accordance with a further feature of the invention there is provided a well drilling apparatus including a mast and means for rotatably supporting a drill string therein. This apparatus includes means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm adapted to grasp and swing individual pipe sections between a generally upwardly directed position at or in the mast and a lower generally horizontal position. The apparatus includes storage means for the sections of drill pipe having a bed for supporting a plurality of layers of generally horizontally disposed pipe sections, the layers being in generally vertically stacked relation. Means are provided for raising or lowering the bed of the pipe storage means thereby to raise or lower the layers of pipe sections supported thereon to enable successive pipe layers to be positioned adjacent the lower, generally horizontal, position taken by the pipe handling arm. Means are provided for individually transferring the sections of pipe from the storage means at the level of said pipe layer to the pipe handling arm for engagement thereby and vice versa.

In the preferred arrangement the pipe storage means are adapted to tilt the bed such that the pipe sections tend to roll towards or away from the pipe handling arm during transferral of the pipe sections into or out of the storage means respectively. In the preferred arrangement the storage means includes a pair of beds located in spaced generally parallel relationship with one another on opposing sides of the lower position taken by the pipe handling arm, the pip handling arm being adapted to receive and grip a drill pipe transferred thereto from either bed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Further aspects and advantages of the present invention will be apparent to those skilled in the art from a reading of the following description of a preferred embodiment of the invention with reference being made to drawings wherein:

FIG. 1 is an elevation view of the mobile drilling rig during a vertical drilling operation;

FIG. 2 is a plan view of the mobile drilling apparatus;

FIG. 3 is an elevation view of the mobile drilling apparatus showing the drill mast in down folded position and the operators cab assembly in a retracted position overlying a portion of the drill stem racking area;

FIG. 4 is an elevation view of the mobile drilling apparatus illustrating the mast in an inclined position for inclined drilling operations;

FIG. 4A illustrates drill stem hoisting and drawdown means;

FIG. 5 is a cross sectional view taken along line 5-5 in FIG. 2 and illustrating the make and break mechanism;

FIG. 6 is a cross sectional view taken along line 6-6 in FIG. 2 illustrating a portion of the pipe gripping means of the pipe handling arm together with the drill pipe racking means;

FIG. 6A is a view of a portion of the structure shown in FIG. 6;

FIG. 7 is a plan view of the pipe racking means;

FIG. 8 is an elevation view of the operators cab and its support assembly;

FIG. 9 is a section view taken along 9-9 in FIG. 8;

FIG. 10 is a detail view of a device for transferring drill pipe into and out of the racking means;

FIG. 1 l is a schematic diagram of a portion of the hydraulic control circuit for the drill pipe rack beams.

GENERAL ARRANGEMENT Referring now to the drawings it will be seen that the drilling unit 10 includes an elongated mobile chassis 12 supported for travel from one site to another on a plurality of wheels 14 having pneumatic tires mounted thereon. Chassis 12 comprises a spaced pair of elongated steel frame members 16 (which, in plan, have the configuration shown by the heavy dashed lines in FIG.

2) and suitable cross members and bracing members (not shown), all designed to give the chassis the necessary structural strength and rigidity. The chassis may be considered as being made up of three regions A, B and C which extend longitudinally of the chassis as shown in FIG. 2. Region A extends longitudinally of the chassis from the front end 18 thereof to a point roughly half way along the length of the chassis and defines a region wherein lengths of drill pipe are stored on suitable racking devices 20 provided for that purpose. Region C extends from the rear end 22 of the chassis towards region A but is separated therefrom by an intermediate region B which is relatively short in comparison with the length of region A or region C. Drill operating machinery 24 including a prime mover, compressor, pumps etc. is supported in region C while an elongated drill mast 26 (which is mounted for movement between a generally horizontal transport position and an upright operating position) and its associated equipment e.g. drill pipe make up and break out equipment 28, are disposed in region B. A swinging pipe handling arm 30 conveys individual sections of drill pipe between a generally horizontal position in the drill pipe storage area and an upright position in mast 26 during drill pipe make up and break out operations. An operators cab 32 is disposed adjacent the front end of the chassis and is mounted for limited movement longitudinally of the chassis in a fashion to be more fully described hereinafter. A plurality of hydraulic levelling jacks 33 are provided on the chassis to assist in levelling the drilling rig and providing support to same during a drilling operation.

As mentioned previously, the drilling unit is preferably designed such that at the commencement of a drilling operation, with a full complement of drill pipe disposed on racking devices 20 and the mast 26 in an operative position, the drilling axis D--D (as shown in FIGS. 1, 4 and 5) passes substantially through the center of gravity of the entire system, the latter comprising the drilling unit together with the drill pipe on the racking means. In any event, it should be designed such that at least 70 percent of the total weight of the system, including the racked drill pipe, is available at start-up to produce downward thrust on the drill. Those skilled in the art will be able to make the necessary calculations to determine the total weight of the drill pipe which the racking devices 20 should be designed to carry at the commencement of a drilling operation as well as the weights of and the relative locations of the various items going to make up the drill operating machinery 24, the drilling mast 26 and its associated equipment, as well as the chassis, the operators cab (such cab being in the extended operating position shown in FIGS. 2 or 4) in order to effect placement of the center of gravity of the system properly relative to the drilling axis.

A notable advantage of the arrangement described above, with the racked drill pipe supported entirely on the drilling unit, is that the drilling apparatus may be transported from one drilling site to another while carrying its own drill pipe; there is usually no need for additional vehicles to carry the drill pipe. This reduces moving and set up costs and makes for a more economical operation.

As the depth of the drilled hole increases, with a corresponding increase in the length of the drill string, the center of gravity of the entire system will gradually shift away from the drilling axis. However, as mentioned previously, this does not create a problem because the weight of the lengthening drill string becomes progressively greater with the result being that adequate downward thrust can be applied to the drill bit at all times. It is at the commencement of drilling operations that the need for the center of gravity of the entire system to be positioned close to or at the drilling axis D-D is the greatest.

DRILL MAST The drill mast 26 is of standard construction, i.e. it is constructed of steel members arranged to define an open lattice work-like structure which is light in weight but at the same time sufficiently strong as to enable it to perform in a satisfactory fashion. Mast 26 includes an open side 34 facing toward the drill pipe racking area whereby lengths of drill pipe may be carried into and out of the mast interior by means of the pipe handling arm 30. The means provided for rotatably supporting the drill string within the mast comprises a power swivel 36 of any suitable construction mounted for movement longitudinally of the mast on spaced rails 38 (see FIG. 5). A cable and pulley system including lifting and drawdown cables arranged to provide the required mechanical advantage is provided for applying lifting or drawdown forces to the power swivel 36 in the manner well known in the prior art. When a drawdown force is being applied to the power swivel 36 a corresponding lifting force is, of course, being applied to the drill unit. Since the drilling axis D-D along which the drill string passes is near to or coincident with the center of gravity of the entire system, virtually the entire weight of said system is applied to the drill string before the drill unit is lifted off the ground by the lifting force referred to above. A powered winch arrangement 40 e.g. a Gearmatic Series 40 winch, mounted on and adjacent the lower end of mast 26 tensions the lift or drawdown cables as required.

The drill mast 26, the power swivel 36 and the means for moving same longitudinally of the mast are shown diagrammatically in FIG. 4A, it being realized that the components shown are not in their usual proportions Prior art details, such as the means for guiding the power swivel longitudinally of the mast etc. are not shown. The powered winch 40 includes a single winch drum which is driven in either direction by winch drive assembly 152. In order to hoist the power swivel 36 upwardly a hoisting line 154 (shown as a solid line) is provided which has its one end connected adjacent one end 150a of the hoisting drum while its opposing end is firmly anchored at 158 to a fixed point on the drilling unit. Hoisting line 154 passes upwardly from winch drum 150 over fixed sheave 160 then around sheave 162 on power swivel 36, around sheaves 164, down around sheave 166 and then over sheave 168 and then down to the anchor point 158. The hoisting arrangement just described is a four string arrangement in that a mechanical advantage of four is provided. The power swivel drawdown arrangement also is a four string arrangement. The drawdown cable 170 (shown as a dashed line) is connected at its one end to winch drum 150 adjacent end (150a) of the latter, and at is other end to an anchor point 176 fixed to the drilling unit. Between these points the cable passes over and around sheaves 171, 172, 173, 174, (sheaves 173 and 175 being mounted on power swivel 36) and then down to anchor point 176. The drawdown and hoist cables 170 and 154 are arranged such that as winch drum 150 is rotated, one of said cables wraps on the drum in a single layer while the other cable unwraps therefrom thus ensuring equal rates of pay out and take up of the two cables at all times thus causing the power swivel to move upwardly or downwardly within the mast 26 to effect lifting or drawdown of the drill string as required.

The power swivel 36 includes suitable hydraulic motors therein to rotatably drive threaded nipple 42 mounted therein, the latter being adapted to screw into the upper end of a drill string and effect rotation thereof, all as well known in the art. Suitable connections to the power swivel 36 are provided to supply hydraulic fluid thereto and to supply drilling fluid to the interior of the drill string and thence to the drill bit.

The mast 26 is supported at its lower end by means of a spaced pair of arms 44 which flank the lower end of the mast. Arms 44 are each pivotally connected to chassis member 16 by pivotal connections 46 with the angle of inclination thereof being determined by the degree of extension of a pair of telescoping braces 47 each interconnected between a respective one of the arms 44 and its associated frame member 16. When the braces 47 are partially retracted or telescoped, arms 44 assume an inclined position with the mast 26 also taking a similar inclination thereby to permit inclined drilling to take place as shown in FIG. 4. The mast 26 is connected to arms 44 by way of groove defining guides 50 which extend along opposed sides of the mast from the lower end thereof to about half way along its length. The grooves of guides 50 engage with pin means 52 mounted in the upper ends of arms 44. To assist in raising and lowering the mast 26, it is convenient to provide a pair of hydraulic rams 48 (one being shown in FIG. 3). When the mast is to be raised, it is slid rearwardly and the end 48a of each ram is connected to mast 26 at points 48b and the ram actuated to cause the mast to pivot upwardly. Lock bolts 55 extending through arms 44 and into mast 26 are used to effect engagement between the lower portion of both the mast and arms 44 when the mast has been aligned with arms 44. When the equipment is being readied for highway travel, lock bolts 55 are withdrawn, the mast is pivoted around to the horizontal position shown in FIGS. 3, hydraulic rams 48 are disconnected and the mast is slid forwardly until pin means 52 reach the ends of the groove defined by guides 50, at which point the top of mast 26 is in the most compact travelling configuration. The end of mast 26 is attached to mast support leg 51 during travelling to prevent oscillation of the mast.

DRILL STRING MAKE UP AND BREAK OUT MECHANISM The drill string make up and break out means 28 is located at the base of the mast 26 and is mounted such that it pivots about the axis defined by pivot pins 46 together with mast support arms 44 as illustrated in FIG. 4. The make up and break out system 28 includes a set of conventional air pressure operated slips 54 (FIG. which are supported by slips support frame 55. Slips 54 are aligned with the drilling axis and are adapted to releasably grip the upper end of the drill string to support the latter within the drill hole. A set of power tongs 56 of any suitable commercially available variety (e.g. Foster" Power Tongs) are disposed above the slips 54,

and are adapted to engage and rotate the drill stem to loosen or tighten the threaded joints between the drill pipes during drill string make up or break out. Tongs 56 are mounted on a torque arm 59 in conventional manner. Below slips 54 is'a drilling nipple 58 through which the drill string passes; flow line 60 is connected to nipple 58 for use in the usual fashion. Those skilled in the art will realize that the nipple 42 of the power swivel 36, the power tongs 56, the slips 54 and drilling nipple 58 are all in alignment with each other along the drilling axis D-D.

PIPE HANDLING ARM The drill pipe handling arm 30 is pivotally connected to the chassis 12 at pivot point 61 which is adjacent the foot of the mast and near to or aligned with the axis defined by pivot pins 46. Handling arm 30 is adapted for movement in a vertical plane between a substantially horizontal position in the drill pipe racking region A and a generally upright position in the drill mast 26 to permit the nipple 42 of the power swivel to screw into or out of the upper end of a length of drill pipe engaged by the pipe handling arm. Pivotal movement of arm 30 is effected by the elongated hydraulic cylinder 60 which is pivotally connected at its one end to the chassis and at its other end at 62 to arm 30. A suitable hydraulic system (not shown) connected to cylinder 60 is used to effect control of the movement of the pipe handling arm. Arm 30 is provided with a spaced apart pair of clamps 64 for grasping individual sections of drill pipe. Each clamp 64 (see FIG. 6) includes a seat member 66 rigidly connected to the arm proper. Pivotally connected to opposing sides of seat 66 are a pair of jaws 68, the movement of each of which is controlled by respective one of two hydraulic cylinders 70, each of the latter being interconnected between rigid member 72 affixed to arm 30 and its associated jaw 68. When jaws 68 are closed, the pipe is securely clamped against seat 66. However, when one jaw or the other opens, jaw portion 69 (FIG. 6) engages the underside of the pipe and lifts it out of seat 66 with the result being that the pipe rolls away from that side of the handling arm on which jaws 68 have opened. This action is clearly illustrated in FIG. 6A,

PIPE RACKING AND TRANSFER SYSTEM As mentioned previously, the drill pipe racking area is located in region A as seen in FIG. 2. The racking device actually comprises two parallel racks and 92 which extend longitudinally of the chassis in laterally spaced relation to one another to define therebetween a longitudinally extending well 94 within which the pipe handling arm 30 is received when it is in the lower, generally horizontal, position. The pipe racks are supported on a pair of transversally extending beams 96, 98 (FIG. 3) spaced longitudinally of and connected beneath the main chassis members 16. The opposing ends 96 98 of each beam 96, 98 project laterally outwardly of the main chassis members, and each of these end portions 96' 98' carries a spaced pair of upright hydraulic jacks 100, 101 (FIG. 6). Each pair of jacks is pivotally connected to an associated rack beam 104. A longitudinally spaced pair of rack beams 104 serve to define the bed of each pipe rack. Actuation of the jacks 100, 101 serves to raise or lower the rack beams 104 in the manner to be hereinafter described. In order to promote stability of the pipe racks 90, 92 the jacks nearest the main chassis members 16 are connected thereto by suitable clamps 106 and the two rack beams 104 of each rack 90 and 92 are connected together by cross braces 108 and brace 110 as shown in FIG. 7. As seen in FIG. 6 several layers of the drill pipe are supported on each of the racks 90 and 92; the layers are separated from one another by suitable spacers 120 so that the pipe sections can roll towards or away from the longitudinal center line of the vehicle depending upon the direction of inclination of the associated pairs of rack beams 104. In order to prevent the pipe sections from rolling off the rack beams 104, upright posts 105 are rigidly connected to the outer end of each beam as best seen in FIG. 6 against which the pipes bear. Each rack 90, 92 further includes respective shelves 122, 124 secured to the machine chassis and arranged in flanking relation to the well 94 between racks 90, 92 as best seen in FIGS. 6 and 7. Shelves 122, 124 serve to rollingly support lengths of pipe as the latter are transferred between the handling arm 30 and the respective racks 90 and 92 and for this purpose they are provided with short, horizontal support zones 126(FIGS. 6, 6A,l0) located just below the elevation taken by a pipe section when the latter is engaged in handling arm 30 with the latter in its lower loading or unloading positron.

Associated with each rack 90, 92 is a pipe transfer assembly 112 each of which includes an upright support post 114 mounted on the outermost end of beam portion 96 (FIG. 6) to which is connected a support arm 116 extending across the width of the rack and having a pipe flipper I18 pivotally connected to the free end thereof closely adjacent the well within which the pipe handling arm is received. Each pipe flipper 118 is adapted to individually engage each pipe section during the process of transferring the sections into or out of the racks. Referring to FIGS. 6 and it will be seen that pivotal movement of each flipper 118 is effected by an air cylinder 130 mounted on support arm 116 to effect pivotal motion of the flipper between the dotted and full line positions thereof seen in FIG. 10. The flipper element includes a finger portion 132 which (a) serves to engage a section of the drill pipe delivered thereto from the handling arm and push same into its associated rack and (b) serves to release a pipe section from the rack so that the section may roll towards the handling arm 30 for engagement thereby. Flipper 118 also includes arcuate portion 134 angularly spaced from finger 132 which engages the pipe section next to the one being transferred into the handling arm 30 and prevents it from rolling towards the pipe handling arm i.e. more than one pipe rolling toward the handling arm at any one time is prevented.

In order to effect raising or lowering of the rack support beams 104 so as to bring each layer of drill pipe up to the level of the shelf means 126, and further to effect tilting of the rack beams 104 so that the individual sections roll towards or away from the pipe handling arm 30, a suitable hydraulic control system is provided. The hydraulic control system is devised such that, when considering one racking area, rack 90 for example, all four hydraulic jacks 100, 101, can be actuated simultaneously so as to lift both racking beams 104 and the drill pipe layers supported thereon by an equal distance. In addition, the hydraulic system should permit the two outer hydraulic jacks 101 to be actuated independently of the two inner hydraulic jacks 100 thereby to permit the racking beams 104 to be tilted in the same direction. For example, beams 104 may be tilted so that the sections roll towards the pipe handling arm 30 i.e. towards the elongated well 94 between the two pipe racks and 92. This action is necessary when going into the hole i.e. when the pipe sections are being removed from the racks and. connected together into a drill string. Alternatively it is necessary to tilt the rack beams 104 so that the individual pipe sections roll away from the pipe handling arm 30(see FIG. 6A) when coming out of the hole" i.e. when the drill string is being broken up into pipe sections and stored in the racking areas. A typical hydraulic system capable of performing as mentioned above is shown in the schematic diagram of FIG. 11 wherein there is illustrated a source of hydraulic pressure 8" connected to two banks of hydraulic control valves X and Y the latter being connected individually to the hydraulic jacks 100, 101 as shown. Bank X controls rack beams 104 of racking area 90 (on the right hand of the machine) while bank Y controls the rack beams on the opposite side of the machine in racking area 92. Each bank of control valves has four valve actuating levers, one for each hydraulic jack 100, 101. However, since one usually desires to operate the hydraulic jacks in pairs to effect bed tilting or all four in unison to raise or lower the beds, suitable means (not shown) may be provided to link pairs of the valve actuating levers together to permit actuation of two hydraulic jacks 101 or to gether to effect tilting motion of the rack beams 104 in unison; suitable means may also be provided to facilitate actuation of all four jacks together to effect raising and lowering in unison of both rack beams 104 as described above.

OPERATORS STATION As mentioned previously the operators station 32 is mounted on the front end of the chassis 12 in such a way that the station is supported for movement from a first position for transportation of the drilling unit with the station overlying the end portion of the racking area 20 to a second operating position displaced outwardly of the end of the racking area whereby ready access may be had to the racking area for addition or withdrawal of drill pipe as the case may be. The operating position of the operators station 32 is illustrated in FIGS. 1, 2, 4 and 8. FIG. 3 illustrates the operators station 32 in the retracted position overlying an end portion of the racking area 20. With this arrangement the overall length of the drilling unit can be reduced when the drilling unit is travelling along public highways or the like. The chassis need thus be made only long enough so as to accommodate the mast, its associated drill operating machinery and the drill pipe racking means 20. Referring particularly to FIGS. 8 and 9 it will be seen that the operators station 32 includes a suitable housing or cab which contains, a steering wheel and other controls so that the operator may control the movement of the drilling unit over public highways. The operators cab is not usually used to house the operators console used to effect control of the various components of the drilling unit during a drilling operation. This control console (not shown) may conveniently be mounted on the side of the drilling unit just forwardly of the mast so that the operator can easily see the components of the machine in operation. The cab, per se, may be of any well known construction and further details of same need not be given here. The cab is mounted on a suitable framework 140 which includes a pair of spaced generally parallel support beams 142 which extend beneath and project rearwardly of the cab unit for a substantial distance. Support beams 142 are spaced apart a distance just slightly less than the spacing between the main chassis members 16 with each of the support beams 142 being located immediately inwardly of a corresponding one of the chassis members 16 in slidable relation therewith as shown in FIGS. 8 and 9. In order to provide for ease of movement of the operators station 32 from the advanced position to the retracted position shown in FIG. 3 and vice versa, a plurality of rollers 144 are mounted on spaced stub shafts secured to the main chassis members 16 and project inwardly from the inner face of the web of each chassis member as shown in FIG. 9. These spaced rollers 144 serve to rollingly support the support beams 142. In order to positively shift the operators station from the retracted position for travelling to the advanced operating position, an elongated hydraulic jack 146 is provided which extends parallel to the longitudinal axis of the chassis and is connected at one end to a transversely extending frame member which interconnects support beams 142 together and at its other end to a transverse frame member interconnecting main chassis members 16.

DRILL OPERATING MACHINERY The previously mentioned drill operating machinery 24 includes a prime mover (e.g. a GM. l2V-7l) diesel engine 74 connected to chain case 76. Chain case 76 has an output connected to air compressor 78 (e.g. an Atlas Copco DR 4l8 or equivalent) and another output connected to transmission 80 (e.g. an Allison TG-64T transmission) via drop box 82. The transmission output may be connected, upon selection, to drive either the rear tandem wheels of the machine via drive shaft 84(FIG. 3) or the hydraulic pumps 86 which, among other things, supply power to the power swivel 36 to effect drill string rotation, or for the winch system for effecting lifting or drawdown of the power swivel 36. A mud pump 88 is also driven from chain case 76. Suitable clutch means (not shown) are provided in the above described power train to permit individual ones or groups of the above mentioned units to be driven at any one time by the prime mover as desired.

It will be seen from the above that since the power source and drive train, including drive shaft 84 and the rearwardly disposed propulsion wheels, are located adjacent the rear of the drilling unit in region C, the central region of the drilling unit, particularly region B wherein the drilling mast and its associated equipment are located, is completely free of drive train components for propelling the mobile drilling unit. This is in contrast to prior art machines which generally have the drive shaft and other various components of the drive train located in the center section of the machine thus placing them in the way of any drilling mast and its associated equipment in this area and necessitating placement of the latter at one end or the other of the drilling unit.

()PERATION OF DRILLING UNIT The operation of the drilling unit will probably be' operation of the device will now be given. After the drilling unit has been located at the desired drilling site and properly levelled, the mast 26 is swung to the vertical operating position shown in FIG. 1; or alternatively if drilling on an incline is to take place the mast is swung to the inclined position shown in FIG. 4. The operators station is advanced, by actuation of hydraulic cylinder 146, to the operating position shown in FIGS. 1 and 4.

At the commencement of the drilling operation it will be recalled that since the racking means 20 contains a full complement of drill pipe, the drilling axis passes substantially through the center of gravity of the entire system so that a major portion of the weight of the entire system is made available to produce downward thrust on the drill bit when drawdown forces are being applied to the power swivel 36. The hydraulic jacks and 101 are actuated relative to one another so that the rack support beams 104 are tilted inwardly toward the center line of the machine so that the individual pipe sections tend to roll toward the pipe handling arm 30. The hydraulic jacks 100, 101 are actuated in unison thereby to bring the uppermost layer of drill pipe to a level just slightly above the upper level of the shelf means 126 as illustrated in FIGS. 6 and 10. The pipe handling arm 30 is then swung by virtue of the action of hydraulic cylinder 60 to its lower horizontal loading position as shown in FIG. 6 and the appropriate set of hydraulic cylinders 70 are actuated so as to cause one jaw 68 of each of the two clamping devices 64 to swing open thereby to enable the pipe handling arm 30 to receive a section of drill pipe. The air cylinder 130 is then actuated so as to cause the flipper 118 to rotate clockwise as shown in FIG. 10 with the result being that a single section of pipe rolls over the spaced pair of shelf defining means and onto the pipe handling arm 30. The jaws 68 are then closed to securely clamp the pipe section and the pipe handling arm 30 is pivoted upwardly through a vertical plane into the open side of drilling mast 26.

The power swivel 36 is then actuated to cause the threaded nipple 42 thereof to screw into the upper internally threaded end of the pipe section. The power tongs S6 and the power slips 54 are held in a retracted or open position so that a drill bit which is attached to the lowermost end of this first section of drill may be passed downwardly therethrough. The jaws 68 of the handling arm 30 are released and rotation of the drill pipe is effected while drawdown forces are applied to the power swivel 36 thus causing the drill to penetrate the earth. Drilling then continues until the upper end of the first section of drill pipe is located between the level of the power tongs 56 and the slips 54. Rotation of the drill pipe is stopped at this position and the power slips 54 may then be closed to support the drilling pipe extending downwardly into the bore hole. The nipple 42 of the power swivel 36 is then screwed out of the upper end of the drill pipe by reversing its direction of rotation and the power swivel 36 is raised by the drawworks to a level above that of the top of the next section of drill pipe to be added. When the power swivel 36 has been raised to its upper position, the pipe handling arm 30 pivots upwardly while grasping a new section of drill pipe and positions it in alignment with both the section of drill pipe in the bore hole and the threaded nipple 42 of power swivel 36. The power swivel then engages the upper end of the new section of drill pipe and the stern handling arm 30 again pivots downwardly as before after disengaging from the new section. The new section of the drill pipe is then lowered into position by the power swivel for its threads to engage matching threads on the section in the bore hole and rotation of the new pipe section is effected to start the joint between the pipe sections with the power tongs 56 then being advanced to close around the drill string to securely tighten the threaded joint between the two pipe sections to the required degree. Power slips 54 are then disengaged and rotation of the drill string by means of the power swivel 36 is effected with drawdown forces again being applied thereto until the upper end of the second section is between the levels of the power tongs 56 and slips 54. The above described operation is repeated over and over again until the desired hole depth is achieved.

In removing the drill string from the bore hole essen tially the reverse procedure is utilized. The drill string is raised by elevating the power swivel 36 until the joint between the uppermost and the next section of drill pipe is below the power tongs S6 and above slips 54. Slips 54 are then engaged to support the drill string in the bore hole and the pipe handling arm 30 is raised to the upright position and the uppermost section of drill pipe securely clamped by clamp means 64 thereon. The power tongs 56 are advanced and closed around the section of pipe just above the joint and the pipe is rotated thereby just sufficiently to disengage the uppermost section from the drill string then in the hole. The power swivel 36 is operated in a reverse direction to disengage its threaded nipple 42 from the upper end of the pipe section. The pipe handling arm which has engaged the pipe then swings downwardly to the horizontal position; the appropriate set of jaws 68 are swung open and the disengaged section rolls downwardly onto the shelf means and thence into the appropriate racking means. Just before the pipe reaches the racking means, the flipper 118 is actuated so thatit occupies the dotted line position shown in FIG. 10. When the pipe section reaches the dotted line position A shown in FIG. 10 the air cylinder 130 is actuated to pivot the flipper 118 counterclockwise with the result being that it is positively pushed into the appropriate racking area. Little force is required here since at this time the appropriate set of hydraulic jacks has been actuated to tilt the rack support beams 104 so that the sections tend to roll away from the center line of the machine towards the upright posts 105 as seen in FIGS. 6 and 6A. When a complete layer of drill pipe has been placed on one of the drill racks, the hydraulic jacks 100, 101 support ing the rack beams 104 of same are lowered in unison and thin spacer members 120 are positioned on top of the newly added layer after which a new layer of pipe is added. The above described process is repeated until all of the drill string has been removed from the bore hole.

It is to be understood that the above disclosure of the preferred embodiment of the invention has been made only by way of example and that numerous changes in the details of construction and the combination and arrangements of parts may be resorted without departing from the spirit and the scope of the invention as hereinafter claimed.

1 claim:

1. A self-propelled drilling unit comprising an elongated chassis, sets of wheels mounted forwardly and rearwardly of said chassis, a drive engine mounted in a region disposed rearwardly of said chassis, on said chassis forwardly of said rearwardly disposed region in spaced relation therewith for storing lengths of drill pipe such that they extend longitudinally of said chassis, a drilling mast connected to said chassis generally between said rearwardly disposed region and the racking means and movable from an upright operating position to a downfolded position for transport, said drill mast including means for rotatably supporting a length of drill string therein, means for rotating a drill string supported in said mast and supplying drawdown or lifting forces thereto, means for adding and removing lengths of drill pipe from a drill string supported in said mast including means for shifting individually said lengths of drill pipe between said racking means and said mast, and a drive train positioned in said rearwardly disposed region and adapted to provide an operable connection of said drive engine either to said rearwardly disposed set of wheels to effect propulsion of the drilling unit or to the means for rotating the drill string.

2. The self propelled portable drilling unit according to claim 1 wherein the forwardly disposed set of wheels is steerable to effect directional control of the vehicle.

3. A mobile drilling unit comprising: an elongated mobile chassis, a drilling mast attached to said chassis and arranged for movement between a downfolded transport position and an operative drilling position, means in said mast for supporting a string of drill pipe parallel to the mast and within a drill hole during a drilling operation, means acting between the drilling unit and the means for supporting the string of drill pipe for applying drawdown forces to the drill string to enable at least a portion of the weight of the drilling unit to be applied to produce downward thrust on the drill string during the drilling operation, a drill pipe racking means supported on said chassis, drilling machinery also mounted on said chassis, said racking means being capable of carrying a sufficient weight of drill pipe and the spacing and the locations of the drilling machinery, drill mast and racking means relative to one another on said chassis being such as to permit a major portion of the combined weight of said drilling unit and the weight of the drill pipe on said racking means to be available during the initial stages of a drilling operation to produce downward thrust on the drill string when said drawdown forces are being applied to the means for supporting the drill string, said drill pipe racking means being supported on a first longitudinally extending region of said chassis, said drilling machinery being mounted on a second region of said chassis longitudinally spaced from said first region, and said drill mast being located generally intermediate said first and second regions.

4. The drilling unit according to claim 3 wherein the drill pipe racking means is arranged to support lengths of said drill pipe such that they extend longitudinally of said chassis.

5. The drilling unit according to claim 3 wherein said drill pipe racking means is constructed and positioned on said chassis such that when the racking means has a full complement of drill pipe thereon the center of gravity of the drilling unit together with the drill pipe on the racking means is sufficiently close to said drilling axis defined by the string of drill pipe as to make at least percent of the total weight of the drilling unitracked drill pipe combination available to produce downward thrust on the drill string.

6. The drilling unit according to claim 3 further comprising means for transferring sections of drill pipe between said drilling mast and said racking means.

7. A mobile drilling unit including an elongated wheeled mobile chassis, a mast mounted on the chassis and means in said mast for supporting a drill string within a drill hole during a drilling operation and effecting drilling movement thereof, a drill pipe racking area extending longitudinally of said chassis for storing lengths of drill pipe thereon, means for pivoting individual lengths of drill pipe between said racking area and said mast during addition or withdrawal of the pipe lengths to or from the drill string, an operators station mounted on said chassis, and means supporting said station for movement from a first position for transportation of the drilling unit overlying a portion of said racking area to a second operating position displaced outwardly of the racking area whereby ready access may be had to lengths of drill pipe lying in the racking area.

8. The drilling unit according to claim 7 wherein the station supporting means is arranged such that the station moves in a path parallel to the longitudinal axis of said chassis.

9. The drilling unit according to claim 8 wherein said supporting means is arranged such that said second position is disposed outwardly of the end of said elongated chassis.

10. The drilling unit according to claim 9 further including means for positively shifting said station from said first position to said second position.

11. The drilling unit according to claim 10 wherein the operators station is defined by an at least partially enclosed cab.

12. The drilling unit according to claim 10 wherein said shifting means includes hydraulic cylinder and ram means.

13. The drilling unit according to claim 10 wherein the supporting means includes means rollingly supporting the operators station for easy movement in its path of travel.

14. Apparatus for drilling wells comprising a mast and means in the mast for supporting a drill string and effecting drilling movement thereof during a drilling operation, means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm adapted to grasp and swing individual pipe sections between a generally upwardly directed position at or in said mast and a lower generally hori zontal position, and storage means for said sections of drill pipe including a bed for supporting a plurality of layers of generally horizontal pipe sections in stacked relation, means for raising or lowering said bed to raise or lower the layers of pipe sections supported thereon to enable a selected one of said layers to be positioned adjacent said lower generally horizontal position taken by the pipe handling arm, and means for individually transferring the pipe sections between said bed and said pipe handling arm when the latter is in said lower gen erally horizontal position.

15. Apparatus according to claim 14 wherein said storage means includes a pair of said beds for supporting said drill pipe, said beds being in spaced generally parallel relation to one another on opposing sides of said lower position taken by said pipe handling arm, the

latter being adapted to receive and grip drill pipe transferred thereto from each one of said beds.

16. Apparatus according to claim 14 wherein the drilling apparatus is mobile, and includes an elongated mobile chassis, the bed of the pipe storage means being mounted on said chassis and arranged to support said drill pipe in parallelism with the longitudinal axis thereof, said mast and said pipe handling arm also being mounted on said chassis with said pipe handling arm adapted to pivot eachsaid drill pipe through a vertical plane extending between said upwardly directed position and said generally horizontal position.

17. Apparatus according to claim 14 wherein said storage means are further adapted to tilt said bed such that the sections tend to roll toward or away from said pipe handling arm during transferral of said sections into or out of said storage means respectively.

18. Apparatus according to claim 17 wherein the means for transferring the drill pipe sections are adapted to transfer individual pipe sections into or out of the uppermost layer of pipe in said stack.

19. A mobile drilling apparatus comprising: an elongated mobile chassis, a drill mast connected to said chassis and adapted to be folded downwardly during transportation, means for rotatably supporting a string of drill pipe within the mast, said last mentioned means being movable longitudinally of said mast, means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm for engaging and swinging individual sections of drill pipe between a loading and unloading position and a position in said mast for addition or withdrawal of the sections to or from the drill string, a rack for supporting said drill pipe such that said pipe extends longitudinally of the chassis, said rack being mounted on said chassis and supported thereby such that said chassis bears the full weight of said rack and the drill stem thereon, means for transferring individual pipe sections between said arm and said rack at the loading and unloading position, and wherein the drilling apparatus further includes drilling machinery including drill string drive means mounted in a first region extending longitudinally of said chassis adjacent one end thereof, said rack for supporting drill pipe being disposed in another region spaced longitudinally of the chassis from said first region with said drill mast being connected to said chassis intermediate said rack and said drilling machinery.

20. Apparatus according to claim 19 wherein said rack comprises a pair of sections spaced transversely of said chassis to define a region therebetween wherein said arm is received at said lower loading position, said arm being adapted to grip pipe transferred thereto from each one of said rack sections.

21. Apparatus according to claim 20 wherein said rack is adapted to rollingly support a layer of the drill pipe thereon and wherein the rack includes a tilting bed arranged to cause the pipe sections to roll under the influence of gravity towards or away from the transferring means during addition or withdrawal respectively of drill pipe from the drill string.

22. Drilling apparatus comprising a mast having means for supporting a drill string therein and effecting drilling motion thereof during a drilling operation and a pipe rack for supporting lengths of drill string generally horizontally, said rack comprising a pair of pipe support beds parallel to and spaced apart from one another and a pipe handling arm adapted to pivot from a first position between said beds to a second position at or in said mast for transferring individual lengths of the pipe between said first and second positions, said pipe handling arm having pipe clamps thereon each comprising a seat and a pair of pivoting jaws on opposing sides of the clamp for holding pipe on said seat and means for removing a pipe from said seat constructed and arranged such that upon opening of said jaw the pipe is caused to roll away from that side of said arm on which the jaws have opened, means for supporting a rolling pipe between said arm and each one of said beds and means for individually engaging each rolling the pipe between said arm and each of the beds comprising shelves located adjacent the first position taken by said pipe to rollingly support the pipe.

24. Apparatus according to claim 23 wherein the means for individually engaging each rolling pipe section comprises pipe flipper elements disposed adjacent said shelves for engaging and shifting rolling sections of pipe into said bed.

25. Apparatus according to claim 24 wherein said pipe support beds are adapted to support a plurality of layers of pipe in stacked relation and include means for raising or lowering said beds to permit the layers of pipe to be brought to the level of said shelves.

26. Mobile drilling equipment comprising an elongated mobile chassis in combination with and supporting the apparatus of claim 25, said pipe support beds 7 being parallel to the longitudinal dimension of the chas- SlS. 

1. A self-propelled drilling unit comprising an elongated chassis, sets of wheels mounted forwardly and rearwardly of said chassis, a drive engine mounted in a region disposed rearwardly of said chassis, on said chassis forwardly of said rearwardly disposed region in spaced relation therewith for storing lengths of drill pipe such that they extend longitudinally of said chassis, a drilling mast connected to said chassis generally between said rearwardly disposed region and the racking means and movable from an upright operating position to a downfolded position for transport, said drill mast including means for rotatably supporting a length of drill string therein, means for rotating a drill string supported in said mast and supplying drawdown or lifting forces thereto, means for adding and removing lengths of drill pipe from a drill string supported in said mast including means for shifting individually said lengths of drill pipe between said racking means and said mast, and a drive train positioned in said rearwardly disposed region and adapted to provide an operable connection of said drive engine either to said rearwardly disposed set of wheels to effect propulsion of the drilling unit or to the means for rotating the drill string.
 2. The self-propelled portable drilling unit according to claim 1 wherein the forwardly disposed set of wheels is steerable to effect directional control of the vehicle.
 3. A mobile drilling unit comprising: an elongated mobile chassis, a drilling mast attached to said chassis and arranged for movement between a downfolded transport position and an operative drilling position, means in said mast for supporting a string of drill pipe parallel to the mast and within a drill hole during a drilling operation, means acting between the drilling unit and the means for supporting the string of drill pipe for applying drawdown forces to the drill string to enable at least a portion of the weight of the drilling unit to be applied to produce downward thrust on the drill string during the drilling operation, a drill pipe racking means supported on said chassis, drilling machinery also mounted on said chassis, said racking means being capable of carrying a sufficient weight of drill pipe and the spacing and the locations of the drilling machinery, drill mast and racking means relative to one another on said chassis being such as to permit a major portion of the combined weight of said drilling unit and the weight of the drill pipe on said racking means to be available during the initial stages of a drilling operation to produce downward thrust on the drill string when said drawdown forces are being applied to the means for supporting the drill string, said drill pipe racking means being supported on a first longitudinally extending region of said chassis, said drilling machinery being mounted on a second region of said chassis longitudinally spaced from said first region, and said drill mast being located generally intermediate said first and second regions.
 4. The drilling unit according to claim 3 wherein the drill pipe racking means is arranged to support lengths of said drill pipe such that they extend longitudinally of said chassis.
 5. The drilling unit according to claim 3 wherein said drill pipe racking means is constructed and positioned on said chassis such that when the rackinG means has a full complement of drill pipe thereon the center of gravity of the drilling unit together with the drill pipe on the racking means is sufficiently close to said drilling axis defined by the string of drill pipe as to make at least 70 percent of the total weight of the drilling unit-racked drill pipe combination available to produce downward thrust on the drill string.
 6. The drilling unit according to claim 3 further comprising means for transferring sections of drill pipe between said drilling mast and said racking means.
 7. A mobile drilling unit including an elongated wheeled mobile chassis, a mast mounted on the chassis and means in said mast for supporting a drill string within a drill hole during a drilling operation and effecting drilling movement thereof, a drill pipe racking area extending longitudinally of said chassis for storing lengths of drill pipe thereon, means for pivoting individual lengths of drill pipe between said racking area and said mast during addition or withdrawal of the pipe lengths to or from the drill string, an operator''s station mounted on said chassis, and means supporting said station for movement from a first position for transportation of the drilling unit overlying a portion of said racking area to a second operating position displaced outwardly of the racking area whereby ready access may be had to lengths of drill pipe lying in the racking area.
 8. The drilling unit according to claim 7 wherein the station supporting means is arranged such that the station moves in a path parallel to the longitudinal axis of said chassis.
 9. The drilling unit according to claim 8 wherein said supporting means is arranged such that said second position is disposed outwardly of the end of said elongated chassis.
 10. The drilling unit according to claim 9 further including means for positively shifting said station from said first position to said second position.
 11. The drilling unit according to claim 10 wherein the operator''s station is defined by an at least partially enclosed cab.
 12. The drilling unit according to claim 10 wherein said shifting means includes hydraulic cylinder and ram means.
 13. The drilling unit according to claim 10 wherein the supporting means includes means rollingly supporting the operator''s station for easy movement in its path of travel.
 14. Apparatus for drilling wells comprising a mast and means in the mast for supporting a drill string and effecting drilling movement thereof during a drilling operation, means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm adapted to grasp and swing individual pipe sections between a generally upwardly directed position at or in said mast and a lower generally horizontal position, and storage means for said sections of drill pipe including a bed for supporting a plurality of layers of generally horizontal pipe sections in stacked relation, means for raising or lowering said bed to raise or lower the layers of pipe sections supported thereon to enable a selected one of said layers to be positioned adjacent said lower generally horizontal position taken by the pipe handling arm, and means for individually transferring the pipe sections between said bed and said pipe handling arm when the latter is in said lower generally horizontal position.
 15. Apparatus according to claim 14 wherein said storage means includes a pair of said beds for supporting said drill pipe, said beds being in spaced generally parallel relation to one another on opposing sides of said lower position taken by said pipe handling arm, the latter being adapted to receive and grip drill pipe transferred thereto from each one of said beds.
 16. Apparatus according to claim 14 wherein the drilling apparatus is mobile, and includes an elongated mobile chassis, the bed of the pipe storage means being mounted on said chassis and arranged to support said drill pipe in parallelism with the longitudinal axis thereof, said mast and said pipe handling arm also being mounted on said chassis with said pipe handling arm adapted to pivot each said drill pipe through a vertical plane extending between said upwardly directed position and said generally horizontal position.
 17. Apparatus according to claim 14 wherein said storage means are further adapted to tilt said bed such that the sections tend to roll toward or away from said pipe handling arm during transferral of said sections into or out of said storage means respectively.
 18. Apparatus according to claim 17 wherein the means for transferring the drill pipe sections are adapted to transfer individual pipe sections into or out of the uppermost layer of pipe in said stack.
 19. A mobile drilling apparatus comprising: an elongated mobile chassis, a drill mast connected to said chassis and adapted to be folded downwardly during transportation, means for rotatably supporting a string of drill pipe within the mast, said last mentioned means being movable longitudinally of said mast, means for adding and withdrawing sections of drill pipe to and from the drill string including a pipe handling arm for engaging and swinging individual sections of drill pipe between a loading and unloading position and a position in said mast for addition or withdrawal of the sections to or from the drill string, a rack for supporting said drill pipe such that said pipe extends longitudinally of the chassis, said rack being mounted on said chassis and supported thereby such that said chassis bears the full weight of said rack and the drill stem thereon, means for transferring individual pipe sections between said arm and said rack at the loading and unloading position, and wherein the drilling apparatus further includes drilling machinery including drill string drive means mounted in a first region extending longitudinally of said chassis adjacent one end thereof, said rack for supporting drill pipe being disposed in another region spaced longitudinally of the chassis from said first region with said drill mast being connected to said chassis intermediate said rack and said drilling machinery.
 20. Apparatus according to claim 19 wherein said rack comprises a pair of sections spaced transversely of said chassis to define a region therebetween wherein said arm is received at said lower loading position, said arm being adapted to grip pipe transferred thereto from each one of said rack sections.
 21. Apparatus according to claim 20 wherein said rack is adapted to rollingly support a layer of the drill pipe thereon and wherein the rack includes a tilting bed arranged to cause the pipe sections to roll under the influence of gravity towards or away from the transferring means during addition or withdrawal respectively of drill pipe from the drill string.
 22. Drilling apparatus comprising a mast having means for supporting a drill string therein and effecting drilling motion thereof during a drilling operation and a pipe rack for supporting lengths of drill string generally horizontally, said rack comprising a pair of pipe support beds parallel to and spaced apart from one another and a pipe handling arm adapted to pivot from a first position between said beds to a second position at or in said mast for transferring individual lengths of the pipe between said first and second positions, said pipe handling arm having pipe clamps thereon each comprising a seat and a pair of pivoting jaws on opposing sides of the clamp for holding pipe on said seat and means for removing a pipe from said seat constructed and arranged such that upon opening of said jaw the pipe is caused to roll away from that side of said arm on which the jaws have opened, means for supporting a rolling pipe between said arm and each one of said beds and means for individually engaging each rolling pipe section to move some positively into said bed.
 23. Apparatus according to claim 22 wherein the means for removing the pipe from the seat comprises a portion on each jaw arranged to contact and lift Said pipe from said seat upon opening of said jaw to cause the lifted pipe to roll away from that side of the arm on which said jaws have opened, the means for supporting the pipe between said arm and each of the beds comprising shelves located adjacent the first position taken by said pipe to rollingly support the pipe.
 24. Apparatus according to claim 23 wherein the means for individually engaging each rolling pipe section comprises pipe flipper elements disposed adjacent said shelves for engaging and shifting rolling sections of pipe into said bed.
 25. Apparatus according to claim 24 wherein said pipe support beds are adapted to support a plurality of layers of pipe in stacked relation and include means for raising or lowering said beds to permit the layers of pipe to be brought to the level of said shelves.
 26. Mobile drilling equipment comprising an elongated mobile chassis in combination with and supporting the apparatus of claim 25, said pipe support beds being parallel to the longitudinal dimension of the chassis. 